Production in a reservoir system is generally the phase that occurs after development of the reservoir, during which reservoir fluids, such as hydrocarbons (oil or gas), are drained from the reservoir. Sanding is an occurrence in which formation solid particles are produced with reservoir fluids. The generic term used to describe small particles of the formation (the rock around a wellbore) which may be produced with the reservoir fluid is “sand.” The term “fines” has been used in some literature. Reservoir formation material generally comprises a rock type having sufficient porosity and permeability to store and transmit reservoir fluids, such as oil or water. Since sedimentary rocks are porous and form under temperature conditions at which fossil remnants (from which hydrocarbons are derived) can be preserved, they are the most common type of reservoir rocks (rather than igneous or metamorphic rocks). Examples of sedimentary rocks include, but are not limited to, conglomerates, sandstones, siltstones, shales, limestone, dolostone, halite (salt), salts, gypsum, and calcium sulfate anhydrite. Sedimentary rocks can include a wide variety of minerals, including but not limited to, quartz, feldspar, calcite, dolomite, and clay group minerals.
Sand production is the migration of the formation sand caused by the flow of reservoir fluids (such as oil) during production. Sand production can result from shear failure or tensile failure within the reservoir formation material. Shear failure can occur when the borehole pressure is significantly reduced (such as later in the life of a well), which increases stress near the wellbore, leading to formation failure. Tensile failure can occur when the porosity and permeability of the reservoir formation material near the wellbore are significantly damaged or when flow rates are extremely high. Under either tensile failure condition, the flowing fluid can exert significant drag forces on individual grains in the formation, which, if excessive, can cause the cementation between individual grains to fail, resulting in tensile failure and sand production.
In many instances, sand production can be undesirable since it can restrict productivity, erode completion components, impede wellbore access, interfere with the operation of downhole equipment, and present significant disposal difficulties. Sand production increases the diameter of the perforation cavity or the borehole, reducing the support around the casing. As a result, perforations collapse, the cavity becomes larger, and eventually production from the wellbore could cease. If sand production is severe, remedial action may be required to control or prevent sand production altogether, such a gravel packing or sand consolidation. In extreme cases, massive sanding can occur, in which the sand production increases uncontrollably, eventually completely eroding the reservoir material forming the foundation of the well.
Conventionally, measures have been put into place early in a reservoir development project to prevent sand production altogether, to the extent possible. For example, unconsolidated formations with multiple producing zones may be completed cased hole. The cased hole completion procedure involves constructing a barrier system around the borehole of the reservoir to prevent or retard the onset or extent of sanding, including cementing steel pipes into the wellbore and using meshes, such as an expandable sand screen technology. Such measures, however, may have a negative impact on well productivity. That is, productivity performance of the cased hole well can be much lower than that of an open hole well. Also, such measures increase the cost of a reservoir development project, since they require resources, time, and labor for implementation.
The allowance of some amount of sand production can aid in increasing well productivity. Therefore, a method for use in predicting sand production from a geomechanical reservoir system would be useful, in that it would allow determination of if and when sand production would occur, and to what extent, early on a well development project. Using these predictions, a reservoir can be constructed and operated such that a limited amount of sand is produced, a cavity generated in the reservoir is substantially sustained, and well productivity is increased.